CC2640怎样进入privileged mode？

CC2640中，有些寄存器只能在privileged mode下写入，但main()进入的都是user mode。怎样切换到privileged mode？

谢谢！

关于ARM M3的privileged mode，请参考这边解释：http://processors.wiki.ti.com/index.php/SYS/BIOS_for_Stellaris_Devices#SYS.2FBIOS_M4_Operating_Modes_and_Stack_Usage

M3 Operating Modes

The Cortex M4 internally supports two operating modes: 'Thread' mode and 'Handler' mode. Within 'Thread' mode, the M4 code can run in either 'Privileged' or 'User' mode. By definition, 'Handler' mode code always runs in 'Privileged' mode.

Within SYS/BIOS:

• Swi and Task threads run in 'Thread' mode.

• Hwi threads run in 'Handler' mode.

• All SYS/BIOS internal code as well as application code (ie Hwi, Swi, and Task threads) run in 'Privileged' code mode.

• For performance reasons, SYS/BIOS does NOT support 'User' code mode.